Sharepoint access requests in Outlook

Hello,

Since a couple of weeks, we are facing a weird issue in the Outlook client. Some of our users can't approve SharePoint access requests in Outlook anymore. Whenever they press "Approve" or "Decline" the following error message is displayed:

In the past we also received this message:

We already tried the following:

- Update Outlook client version (2202->2208->2212) all share same behavior

- Recreate Outlook profile 

- Test in Outlook Web (no issue here)

- Sign in on a different client with affected account (no issue here)

Maybe somebody has an idea?

Thank you